by Matthew McCullough of Ambient Ideas, LLC

with DVCSGit going

50 minutes of mental spoon bending

via source code control

DVCS

What? Why?

Basic Use

Who? GUI

Theory

Sharing

Interop High Points

Git-nounBritish Slang. an unpleasant or

contemptible person

-Oxford English Dictionary

“

”

≉

I'm an egotistical bastard, and

I name all my projects

after myself. First Linux,

now git.-Linus Torvalds

“

”now git.

CVS

BitKeeperSubversion

PVCS

Perforce

ClearCaseSource

Safe

Mercurial

Bazaar

RCS

Folders

darcs

GitSource Code Control

CultureChange

CentralizedVCS =Don’t

DoWhatever!DistributedVCS =

InnovateExperiment

Safely Be WrongDrive-by AssistCrowd Source

Crowd Source

① Download binaries

Win Cygwin

Win msysGit

Linux Source

Linux Package manager

Mac MacPorts

Mac git-osx-installer

Any JGit

Git Distro Sources

② Put it in your path

③ Identify yourself

git config --global user.name "Hal Smith"

git config --global user.email "hal@bnl.com"

Global Git Settings

④ Use it!

mkdir myproj.git

cd myproj.git

git init

Creating a Repo

Just show it to me!

CertifiedGit User

145+ Commands

Follow theDOTS

Symmetric

subversion server

developer A developer B

chec

k in

update

check in

upda

te

Symmetric

Distributed

developer A developer B

blessed repo

developer A developer B

commitcommitcommit

commitcommit

commit commit

delete delete

rebase

push

push

push

push

pull

pull

Distributed

WorkingOffline

More available connectivity

More demand to work without connectivity

CheckinAddBranchList change logGrep historyRewrite historyStashMergeLabelRemovepractically everything but push

Offline Anything

Cool! Another commit to my latest OSS

project using Git!

I liked subversion better...

DVCS

What? Why?

Basic Use

Who? GUIs

Theory

Sharing

Interop High Points

Who’s Got Git?

GUIs

GitX

GitSafe

GitK

GitGUI

EGit

It’s Officia

l!

UsageModels

Central Repo

Ce

nt

ra

liz

ed

Blessed Repo

Dic

ta

to

rs

hip

Certified Repo

Development Repo

Int

eg

ra

tio

n M

an

ag

ed

Mirror

Development Repo

Mir

ro

re

d

Mirror

Certified Repo

Cu

st

om

+ P

ub

lic

Co

nt

rib

Customized

☚ P

riva

te

Pub

lic ☛

GitHub

Hashes and Git

‣Centralized VCS uses DB sequential index.

Index vs Hash

‣Git uses SHA-1 hash.

Index vs Hash

I thought

hashes were

for

passwords?

‣ Different goals.‣ Hash for the sake of integrity.‣ Hash for the sake of identity.

SHA-1 Hash

40 hex characters

Use as little of it as is unique

Treeish

Shorthand for the hashes

9AB223

9AB223^

9AB223..56CD77

HEAD

HEAD^

HEAD~3

But I’ve been

hearing news

about hash

collisions...

earth atoms10

49

SHA11046

stars10

22

sand grains10

20

collision10

19

‣Blob‣Tree‣Commit‣Tag

Hashable Objects

http://book.git-scm.com/1_the_git_object_model.html

Integrity‣ Identifies damaged repos.‣ Prevents modification of published history.‣ Unique to file size and contents.

Hash Benefits

Tags‣ Cryptographically sign tags by GPG.‣ Guarantee repo’s state at a point in time.

Hash Benefits

Storage Mechanics

Typical SCMs use delta storage

CVS / Subversion / darcs / Mercurial

Checkin

Checkin Checkin Che

ckin

Che

ckin

Che

ckin

Che

ckin

Che

ckin

Check

in

Checkin

Checkin

Delta storage gets slower as the history of a file gets longer

Git uses DAG storage

Directed Acyclic Graph

Copy of the entire tree per checkin

cp -r srcfolder srcfolder.prev

Sounds inefficient...

zlib deflates every blob at commit

I’ve had a

400MB Subversion repo

convert to a 70MB Git repo

Speed

git: git

hg: mercurial

bzr: bazaar

data from http://whygitisbetterthanx.com/#git-is-fast

git hg bzr

Init

git hg bzr

Add

git hg bzr

Status

git hg bzr

Diff

git hg bzr

Tag

git hg bzr

Log

git hg bzr

Commit (Lg)

git hg bzr

Commit (Sm)

git c git h hg c hg h bzr c bzr h

Branch (Cold/Hot)

bazaar numbers plus network latency

subversion =

to100 timesFaster

10

Location,Location,Location

Three Stage Thinkingof Git

Git‣ git add‣ git commit‣ git push

‣ Commits only what is added to the index.‣ Opportunity to rewrite history locally.‣ Provides time to change your mind.‣ Selectively share with other repos.

Git‣ git stash‣ git stash apply

‣ Save work-in-progress temporarily, but safely.

‣ Merge stashed modifications back in.

Repo

is like a special

IndexWorking

Stash

git clone

git checkout

edit experiment files

git stash

test buggy files

git stash apply

git add

git commit

Rem

ote

git push

git clone git://somedomain/myproj.gitcd myproj.git

git checkout master

echo ‘//Comments’ >> ClassOne.javaecho ‘//Thoughts’ >> ClassTwo.java

git add ClassOne.javagit commit -m’Added comments’

git stash

◀Build repo

◀Update index

◀Edit working

◀Add to index

◀Save to repo

◀Push to stash

Merge & Rebase

git branch newbranchgit checkout -b newer remote/branchnm

Cheap Branches

git show-branch --allgit branch -a

Cheap Branches

‣Local branch‣localbranchname

‣Remote branch‣remote/branchname

git merge --no-commit <sourcebranch>git merge --squash <sourcebranch>git merge <sourcebranch1> <sourcebranch2>

Merge Anything

git checkout myfeaturebranchgit rebase master

Rebase for Clarity

‣Fast forwards the “side” branch.‣Reposition your feature branch’s start point.

‣See “how trunk will act” before you merge.

‣Makes for simpler merge graphs.‣Cleaner history than a merge.

Rebase for Clarity

Standard

Mergea32

2e2

e69

d19

8b3

Branch

Mas

ter/

Trun

k/M

ainL

ates

t

9f1Merg

e

Rebasing

a32

2e2

e69

d19

8b3

Branch

Mas

ter/

Trun

k/M

ainL

ates

t

a32

2e2

e69

d19

8b3 Branch

Mas

ter/

Trun

k/M

ainL

ates

t

Rebase

a32

2e2

e69

d19

8b3 Branch

Mas

ter/

Trun

k/M

ainL

ates

t

e69

d19 Merge

DVCS

What? Why?

Basic Use

Who? GUIs

Theory

Sharing

Interop High Points

Sharing

Protocols‣ GIT‣ SSH‣ SCP

‣ Local file system‣ SAMBA

‣ HTTP‣ WebDAV

‣ rsync

Serving It Up

git clone git://somehost.org/myproj.git

git clone mccm06@somehost.org:myproj.git

git clone http://somehost.org/myproj.git

git clone ~/work/myproj.git

git clone z:\someserver\myproj.git

◀git daemon

◀SSH

◀HTTP

◀Filesystem

◀Network drive

‣ git instaweb. Built in, read-only, HTTP.

‣ git daemon. Custom socket language.

‣ gitosis. Easy permissions control.

‣ github. Open source & private repos.

‣ ssh. OS controlled permissions.

Serving It Up

SVN Interop

git svn clone http://unfurl.com/trunkgit svn dcommit

Subversion

‣ First class compatibility.

‣ Round trip support.

‣ Git commits = svn commits.

Subversion

‣ git svn clone

Migration

‣ Power off your Subversion server.

Migration

reasons3

❸‣git cherry-pick a5b2ee

‣Merge in just one commit.

Cherry Pick

❷‣git grep SomeText HEAD^^^

‣Search blob contents history without checkouts.

Search History

❶‣git bisect run mvn test

‣Binary-search for bug.

‣Manual or automated modes.

Bisect Bugs

emergingVersion Control System

MatthewTwitter @matthewmccull

Blog http://www.ambientideas.com/blog sidebar has all my social media links

Email matthewm@ambientideas.com

GitHub http://github.com/matthewmccullough

Git Homepagehttp://git-scm.com

Directed Acrylic Graphhttp://en.wikipedia.org/wiki/Directed_acyclic_graph

Git for Computer Scientistshttp://eagain.net/articles/git-for-computer-scientists/

Git Treeishhttp://book.git-scm.com/4_git_treeishes.html

Resources

Git Docshttp://www.kernel.org/pub/software/scm/git/docs/

Git Magic eBookhttp://www-cs-students.stanford.edu/~blynn/gitmagic/book.pdf

Linus Torvald’s Git talk at Googlehttp://www.youtube.com/watch?v=4XpnKHJAok8

CygWinhttp://www.cygwin.com

Resources

MSysGithttp://code.google.com/p/msysgit

Git Cheetahhttp://code.google.com/p/msysgit/wiki/GitCheetah

Matthew’s Git Bookmarkshttp://delicious.com/matthew.mccullough/git

Matthew’s Bash Prompthttp://gist.github.com/47267

Resources

‣ http://www.ambientideasphotography.com‣ http://flickr.com/photos/lenore-m/2903856664/‣ http://en.wikipedia.org/wiki/Git_(software)‣ http://flickr.com/photos/karenhorton/1583513014/‣ http://flickr.com/photos/mashdnart/2545782407/‣ http://commons.wikimedia.org/wiki/

File:Small_Boy_nuclear_test_1962.jpg‣ http://www.flickr.com/photos/knmurphy/2506896257/‣ http://www.flickr.com/photos/albyspace/1022035568/‣ http://flickr.com/photos/michaelhays/3070238360/‣ http://flickr.com/photos/d_vdm/509996632/

Image Credits